Anal Bioanal Chem (2011) 401:2609–2616 DOI 10.1007/s00216-011-5376-6
ORIGINAL PAPER
Triacylglycerol profiling of microalgae strains for biofuel feedstock by liquid chromatography–high-resolution mass spectrometry Karen M. MacDougall & Jesse McNichol & Patrick J. McGinn & Stephen J. B. O’Leary & Jeremy E. Melanson
Received: 29 June 2011 / Revised: 25 August 2011 / Accepted: 29 August 2011 / Published online: 14 September 2011 # The Author(s) 2011. This article is published with open access at Springerlink.com
Abstract Biofuels from photosynthetic microalgae are quickly gaining interest as a viable carbon-neutral energy source. Typically, characterization of algal feedstock involves breaking down triacylglycerols (TAG) and other intact lipids, followed by derivatization of the fatty acids to fatty acid methyl esters prior to analysis by gas chromatography (GC). However, knowledge of the intact lipid profile could offer significant advantages for discovery stage biofuel research such as the selection of an algal strain or the optimization of growth and extraction conditions. Herein, lipid extracts from microalgae were directly analyzed by ultra-high pressure liquid chromatography– mass spectrometry (UHPLC-MS) using a benchtop Orbitrap mass spectrometer. Phospholipids, glycolipids, and TAGs were analyzed in the same chromatographic run, using a combination of accurate mass and diagnostic fragment ions for identification. Using this approach, greater than 100 unique TAGs were identified over the six algal strains studied and TAG profiles were obtained to assess their potential for biofuel applications. Under the growth conditions employed, Botryococcus braunii and Scenedesmus obliquus yielded the most comprehensive TAG profile with a high abundance of TAGs containing oleic acid. Keywords Microalgae . Biofuels . Triacylglyerols . Liquid chromatography . Mass spectrometry K. M. MacDougall : J. McNichol : P. J. McGinn : S. J. B. O’Leary : J. E. Melanson (*) National Research Council of Canada, Institute for Marine Biosciences, 1411 Oxford St., Halifax, NS B3H 3Z1, Canada e-mail:
[email protected]
Introduction Diminishing global oil reserves and increased awareness of the environmental impact of burning fossil fuels have prompted renewed interest in the development of alternative fuel sources in recent years. The viability of microalgae as a carbon-neutral biofuel source has been well documented [1–4]. In contrast to land-based biomass, microalgae do not compete with food crops for arable land [5, 6] and can grow year-long in photobioreactors with an annual biomass productivity exceeding that of terrestrial plants [7, 8]. Additional benefits of using algae as a biofuel feedstock include possible coupling with waste-water treatment [9] and carbon dioxide sequestration [10, 11]. Despite this potential, algal biofuel production has not yet reached that of terrestrial biomass due to high production costs and energy requirements [12]. For these reasons, research has been devoted to optimizing the algae growth conditions, harvesting conditions, and lipid extraction processes [1]. As new technology is developed and oil prices continue to rise, experts believe that microalgal biofuels will become economically feasible within the next 10 to 15 years [12]. Depending on the strain of microalgae, these singlecelled marine and freshwater organisms are capable of producing lipids at levels up to 20–50% of their dry cell weight under specific growth conditions [2]. These neutral lipids, mainly in the form of triacylglycerols (TAGs), can be converted to fatty acid methyl esters (FAMEs) and used as biofuel, much like lipids from terrestrial plants. In addition to TAGs, the lipid fraction of microalgae may also include chlorophylls, carotenoids, glycolipids, phospholipids, and sterols. Under optimal growth conditions, algae synthesize fatty acids for the production of membrane lipids, which include glycolipids and phospholipids. However, under
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stressed conditions, algae alter their biosynthetic pathways and begin to produce neutral lipids for energy storage, mainly in the form of TAGs [2, 5, 13]. Triacylglycerols are preferred over phospholipids or glycolipids for biofuel production due to their higher percentage of fatty acids and their lack of phosphorous and sulfur. Phosphate hinders the transesterification process, and it has been reported that TAGs have >99% biodiesel yield compared to
